"It will then take its position on this issue in an objective and fair manner. According to the investigation results, China will not protect anyone." Mr Wen met Mr Lee at the presidential Blue House on Friday afternoon, a day before a three-way summit that will also include the Japanese Prime Minister, Yukio Hatoyama.

Japan has already condemned the sinking and announced on Friday it was tightening financial sanctions against the North whose near-bankrupt economy has already been brought to its knees by previous rounds of UN sanctions.

South Korean government officials said Mr Lee would set out South Korea's case for action against Pyongyang which, with US backing, it intends to report to the UN security council as early as next week.

"South Korea is fully concentrating on diplomatic efforts to hold North Korea responsible," Mr Lee's spokesman said in a statement, adding the matter would be discussed on Friday, at the weekend summit and at a security meeting in Singapore in early June.

The meeting comes a week after an international inquiry team held North Korea responsible for torpedoing the Cheonan in a disputed area of the Yellow Sea, producing the tail section of a North Korean-made torpedo as evidence.

China has pointedly refused to condemn the North for the attack which it described as a "tragedy" but urged that both sides resort to dialogue, not confrontation, to resolve the matter.

This week both North and South announced they were suspending trade links in during tit-for-tat exchanges which have seen relations on the Korean peninsular reach their lowest point for a decade.

On Thursday South Korea conducted live-firing anti-submarine warfare drills in the Yellow Sea while the North continued to deny responsibility for the sinking and promised "all out war" if Seoul seeks to take revenge for the loss of the Cheonan.

Two days of intensive talks in Beijing between US and Chinese negotiators failed to find agreement on how to punish Pyongyang, but US diplomats on Wednesday expressed hope that this weekend's talks could see China start to shift its position.

However Chinese analysts said that Beijing was still unlikely to take sides against its erstwhile ally.

"China feels it's on the backfoot and has to find a more active posture on the Cheonan incident," said Zhang Liangui, an expert on North Korea at the Central Party School, a training school for officials in Beijing.

"It's difficult even for China to influence North Korea's behaviour. But China will also hope that South Korea steps back so that confrontation can cool down," he said.

More likely, said Wei Zhijiang, a Chinese expert on Korea from Zhongshan University in southern China who is now a visiting scholar in Tokyo, is that China will agree to abstain from any vote in the UN censuring the regime of Kim Jong-il.

"If South Korea and the United States really take this to the Security Council, then China won't want to have a falling out with them but won't want more sanctions over this, so an abstention vote seems likely," he added.

Russia, the other veto-holding power on the Security Council has also refused to rush to condemn Pyongyang and was sending experts to Seoul to study the findings of the investigation into the ship disaster, the Kremlin said.